US2164650A - Heating plate device - Google Patents

Description

R. s. GOLQDTHWAITE HEATING PLATE DEV IO E Fild Jan. 16, 1937 zdkllllllllllllllll llllll ri ATTORNEYS.

Patented 4, 1939 UNITED STATES HEATING PLATE DEVICE Robert S. Goldthwaite,

Marion, Ind., assignor to Rutenber Electric Company, Marion, Ind., a

corporation Application January 16, 1937, Serial No. 120,937

1 Claim.

This invention relates to an electric heating plate.

By the terminology plate, the same does not necessarily apply to a plane structure.

The chief object of the invention is to simplify the construction of a heating device, commonly known as an electric heating plate, and to strengthen the same.

Another object of the invention is to produce a construction of the aforesaid character in a relatively simple, economical and expeditious manner.

The chief feature of the invention consists in the formation of a heating plate of the character briefly set forth hereinbefore, and more fully set forth hereinafter and in a manner hereinafter to be more fully described.

The full nature of the invention will be more fully understood from the accompanying drawing and the following description and claim:

In the drawing,

Fig. 1 is a top plan view of an electric heating plate shown circular in outline and parts being diagrammatically indicated therein.

Fig. 2 is an end elevation of the plate shown in Fig. 1, parts being broken away to show the same and other parts in central section.

Fig. 3 is an enlarged transverse section through one form of heating plate structure.

Fig. 4 is a similar view of a modified form of heating plate structure.

Fig. 5 is an enlarged sectional view through a plurality of adjacent portions of the same strips embodied in the invention, following the winding operation.

Fig. 6 is a similar view of the same parts following the insulating step and previous to the application of the cover or supporting plate thereto.

In the drawing indicates a metal heating plate, H a shell, and I2 a back plate. As shown in Fig. 2, the back plate rests on the flange Ila of the shell and the adjacent edges of the shell and top or cover plate are suitably secured together by press-fitting, welding, or the like, as 45 indicated at Illa.

In Fig. 3 similar numerals increased by one hundred, indicate like or similar parts and in this figure the plate H0 is welded to the flange lllb of the shell HI having the spaced and inwardly directed flange Illa which supports the back plate I I2.

In Fig. 4, similar numerals of the two hundred series indicate like parts. In this form, the top plate 2 It has a downwardly directed groove forming portion ZlUa adapted to nest the outwardly directed flange 2| lb of the shell 2H having the inwardly directed lower flange 2i la, upon which rests the back plate 2l2. In the chamber thus formed, substantially all of the space not occupied by the members hereinafter to be described, is filled with a suitable heat and electrical insulation, such as mineral wool, indicated in Fig. 2 by the numeral I 3 and in Fig. 3 by the numeral H3 and in Fig. 4 by the numeral 2l3.

In Fig. 2 of the drawing, there is illustrated 10 a metallic ribbon I 4 which is arranged in scroll formation, as shown diagrammatically in Fig. 1. The same is suitably secured as at Iii-that is, its adjacent lateral edge is welded, brazed, or the like, to the cover or vessel supporting plate It). In the channel formed between adjacent portions [4 is positioned a heating element in the form of a strip of resistance material 5. The width of the strip [6 as shown clearly in Fig. 2, is less than the width of the metal strip [4. In other words, the heating element or strip I6 is nested between adjacent portions of the heat conducting strip M which also serves as a reenforcement for the cover or heating plate Ill. The strip l4 serves to confine the heat and localize it so that it is imparted to the strip 14 and thence directly conducted to the plate 1!], except that portion of the heat which rises directly upwardly toward the plate Ill. The heat which is directed downwardly is prevented, to a greater or less degree, from being transmitted to plate 12 by the mineral wool insulation 13, or the like.

In one form of the invention portions I4 may be cast integral with the plate I0 and the heating strip 16 when suitably enveloped by electrical insulation, may be nested in the groove or channel formed by the aforesaid.

The inner end of the scroll arranged heating strip includes an angular extension I! which projects through an aperture IS in an insulating member [9 mounted in the aperture 20 in the plate l2.

Suitably secured to the plate l2 as at 2| is a bracket 22 that mounts a screw bolt 23 bearing a nut 24 thereon. The screw bolt 23 is insulated from the bracket by suitable insulation washers 25. One current conducting line may be clamped between the nut 24 and the metal washer 26. The lead wire portion ll of the heating strip is clamped between the washers 2! and 28.

A similar type of terminal structure is associated with the opposite end of the heating wire, the lead-in portion being indicated by the numeral 29, with the offset portion thereof by the numeral 30 and the same extends beneath the 55 plate to the end of the strip It in the outer channel or groove, as indicated at 3I. The lead-in strip 29 is suitably insulated from the back plate I2 as at 32.

In Fig. 3 of the drawing, the reenforcing and thermal conducting metal strip is indicated by the numeral H4. The adjacent edge of the same is connected as at H5 to the cover or vessel supporting plate I I0. Positioned in the groove 01 channel between adjacent portions of the strip H4, is the electric heating strip H6. The strips lI4I I6 are of dissimilar width. The two strips are superimposed upon each other with a strip of insulation I35 and another strip of insulation I35. The entire superposed strip arrangement is then Wound on a suitable mandrel and thus the electric heating strip is electrically insulated from the reenforcing strip. As shown clearly in Fig. 3, when the strips are associated in wound relation, they are tightly associated together and form a unit with the channel, as it were, between adjacent-portions of the strip I I4and above the upper and lateral edge of the heating strip H6.

The electrical insulating strips I35 originally may be metallic magnesium ribbon, subsequently oxidized for use.

Before securing the heat conducting portions IM to the cover or vessel supporting plate I I0, this channel may be filled with magnesium oxide providing insulation I36 between the cover plate and the electric heating strip. The cover plate, as will be apparent, protects the electric heating strip from water, or the like, from a vessel, such as a coffee pot, et cetera, overflowing and shorting out sections of the heating unit. It will be apparent when the portions I I4 are secured to the cover I IEI that the heating element and the unit as an entirety is'rigidly held together by the cover plate.

In Fig. i a slightly modified form of the invention is illustrated. In this form of the invention, the strip 2M again is of greater width than the heating strip 2I6. However, in this instance, the thermal conducting metal strip 2 I I is provided with a groove or channel 2M0. adapted to nest, partially or completely, as desired, depending upon the depth of the channel or groove 2!, the electric heating strip 2I6. .Interposed between the electric heating strip 2I6 and the metal'strip 2 are strips of insulating material 235.

The four strips are simultaneously wound upon a mandrel and since the insulation strips are of lesser width than the heat conducting and reenforcing strip, the structure when assembled is such that relative transverse movement of the heating strip with respect to the heat conducting strip is prevented. Thereupon the heating unit may have the lateral and upper edge of the strip 2M suitablysecured or united tothe cover plate 2 Ill as at 2I5.

The insulation strips in each of the before The heating'strip again is illustrated as being of a less width than the thermal conducting strip and the insulation strips are each illustrated as being of greater width than the heating strip but of less width than the thermal conducting strip.

After being wound into a heating unit, the insulation strips 335 may have their channel exposed portions 3350. directed inwardly and have their ends contact as at 33517. sufiicient insulation to prevent the electric heating strip from contacting the cover plate and shorting out. If desired, additional insulation, as indicated at 336, may be supplied, this being in the form of the magnesium oxide or any equivalent material. Following the formation of the unit, as shown in Fig. 6, the heat conducting strip 3M is suitably secured to the cover or support plate. I

One form'of insulating strip isof mica material. The resulting construction, how so ever formed, forms a heating plate in which heat is generated in the ribbon wire or heating strip and by reag son of its shape, provides a greater amount of surface per unit of cross section and in this way, the heating strip per unit of length has a greater surface for heat emanation. Likewise, this construction provides that all points of the surface of the heating strip are within a relatively short distance of heat conducting metal so that the heat may be readily conducted away from the source to the cover or vessel supporting plate. This results in the temperature of the heating strip or wire being kept relatively low and this adds to the length of life of the wire. Since the heat generated by the same is concentrated on the cover or vessel supporting plate, the elflciency of this type of heating device is much greater than similar heating devices, heretofore employed in the art.

One suitable form of uniting the thermal conducting strip to the cover or plate is by a copper brazing process which results in a highly efficient thermal bond as well as a mechanical bond. In place of the mineral wool, previously described as useful for filling the chamber of the heating device and designated by numerals I3, H3 and 2I3 in Figs. 2, 3 and 4, respectively, the same may be of asbestos character or a pulverized form of other suitable material.

One problem inherent in the construction disclosed herein, is that it is desired to position the heating strip as close to the cover or plate as possible. Hence, danger of shorting the electric heating strip by its slippage and contacting the cover plate must be positively prevented by any one of the disclosures set forth herein or one of equivalent character.

Inasmuch as the insulation material filling the chamber of the device has considerable thickness below the heating portion of the device, more especially the heating unit, shorting between the electric heating strip and the back plate is not a problem and hence, no special provision for insulation-other than that shown or described is deemed necessary.

-As indicated-at I36 and 336 in Figs. 3 and 6, respectively, magnesium oxide powder may be placed in these grooves, the cover plate superposed upon the thermal conducting strip and then the two united in any'desired and suitable manner.

Increased efficiencyiof the device is also obtained by making the interior surface of the back plate of non-tarnishing character by either making the plate of non-tarnishing material and mechanically polishing the same or by coating the interior face of the back plate with suitable pro- This forms a tective material so that its surface is bright and will remain so. Such a bright or polished surface, therefore, Will reflect any and all heat rays directed upon it from the heating strip H6 upwardly and away from it and thus toward the cover plate.

The terminology adjacent non-continuous portions is intended to refer to portions in the same strip which are adjacent each other and spaced apart as in a spiral or scroll by the dis tance between adjacent portions in a radial plane as distinguished for adjacent portions in immediate continuity.

While the invention has been described in great detail in the foregoing specification, the same is to be considered as illustrative and not restrictive in character. Various modifications have been illustrated and described herein and these modifications as Well as others suggested herein and others Which will readily suggest themselves to persons skilled in this art, are considered to be Within the broad scope of the invention, reference being had to the appended claim.

The invention claimed is:

An electric heating device including, a vessel or like supporting heat transmitting plate of comparatively thin section in thickness and of great area, means supporting said cover plate at its peripheral edge, an elongated continuous electric heating strip beneath the plate and of bare metallic resistance type ribbon of rectangular like section and Wound on edge with one of its edges adjacent and substantially parallel to the cover plate, a corresponding heat conducting metal strip in juxtaposition to the heating strip, rigid with the cover for reenforcement thereof against Warpage and correspondingly Wound and having a corresponding edge in direct thermal contact with the cover for thermal conductivity, means electrically insulating the heating strip from the cover and the juxtapositioned reen-- forcing strip, the two strips being of scroll outline, the heat conducting strip including a groove in one side face thereof for laterally nesting the heating strip therein for locating purposes, the insulation means being at both sides of the heating strip, the strips and insulation being coiled into a compact mass, the heat conducting strip including a projecting portion at one side of the groove for rigid connection to the cover, and a heat deflecting plate beneath the heating and metal strips and spaced from the heating strip and associated with the cover supporting means.

ROBERT S. GOLDTHWAITE.

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